The present invention generally relates to a steering control apparatus and method for a vehicle having a continuously variable transmission. More particularly, present invention relates to a steering control device or system in which a steering wheel and a transmission operating device can combine to control a pair of left and right continuously variable transmissions such that the vehicle has zero turning radius (ZTR) capability.
Many types of vehicles, and particularly utility vehicles such as lawnmowers, tractors and the like, are steered to the left and right through the operation of independently controlled drive wheels. For instance, to turn such a vehicle to the left, the left drive wheel can be slowed relative to the right drive wheel such that the greater percentage of torque produced by the vehicle""s motor is transmitted to the right drive wheel. One popular technique for independently controlling the drive wheels is to employ a transmission system in which separate continuously variable transmission (CVT) devices respectively control each drive wheel. The CVT devices are typically controlled by a pair of hand-operated levers, foot-operated pedals, or the like. In addition to transmission-controlled steering systems, these types of vehicles can also rely on their steering wheels to turn non-driven wheels in a conventional manner. Recently, some of these vehicles are capable of executing zero radius turns to provide greater maneuverability.
In commonly assigned U.S. Pat. No. 5,850,886 to Kuono et al., the content of which is incorporated herein in its entirety, a vehicle equipped with a useful CVT-controlled steering system is disclosed. The vehicle includes a steering wheel linked to a pair of non-driven front wheels, and a pair of rear drive wheels controlled by a corresponding pair of CVT devices. The steering wheel not only controls the non-driven front wheels, but also controls the CVT devices and thus the rear drive wheels through a pair of cables such as Bowden wires that actuate a transmission control system. The ability to control the CVT devices by means of the steering wheel is highly advantageous in the mass consumer market, because the steering wheel constitutes a steering control interface with which consumers are generally familiar and comfortable.
While the steering wheel-controlled transmission system disclosed in U.S. Pat. No. 5,850,886 is advantageous, it is not designed to provide its vehicle with zero turn radius capability. It would therefore be advantageous to provide an apparatus and method for steering a vehicle using a steering wheel controlled transmission system, and also provide the apparatus with the ability to steer the vehicle at a zero turn radius.
The present invention in general terms provides an apparatus and method for steering a vehicle with zero turning radius capability. The invention is particularly advantageous as applied to a riding-type vehicle, such as a lawnmower, tractor, or other utility vehicle having at least a pair of left and right drive wheels and one or more non-driven wheels. The apparatus generally comprises a steering handle such as a steering wheel, a transmission control device, and a pair of continuously variable transmission devices. The steering handle and transmission control device are intercoupled through a suitable steering linkage assembly, which preferably includes a pair of cables such as Bowden wires. The steering handle preferably is not linked to any wheels of the vehicle, such that the vehicle is turned solely by means of the interactive operation of the steering handle, the transmission control device, and the continuously variable transmission devices. Preferably, in addition to the drive wheels, the vehicle comprises one or more non-driven wheels that are provided as caster wheels. The caster wheels swivel freely in response to turning of the vehicle, and independently of the operation of the steering handle. The caster wheels advantageously facilitate the steering of the vehicle at a zero turn radius. The zero turn radius capability of the vehicle is described in detail hereinbelow.
By moving the steering handle in a desired direction, such as by turning a steering wheel, one of the cables of the steering linkage assembly actuates certain components of the transmission control device in a manner that adjusts the respective states of the continuously variable transmission devices. Each continuously variable transmission device controls an individual drive wheel of the vehicle and, more specifically, controls the angular velocity of each drive wheel in terms of both rotational speed and direction (forward or reverse) of rotation. Thus, for instance, if the steering handle is turned to the left while the vehicle is being driven forwardly, the transmission control device is actuated so as to cause one of the continuously variable transmission devices to drive the right drive wheel at a relatively fast speed in the forward direction, while the other continuously variable transmission device drives the left drive wheel either at a slower forward speed, at a zero speed (i.e., a neutral state of the left drive wheel), or even at a reverse speed. The vehicle is turned or steered as a result of the differential angular velocities of the drive wheels. In the case of driving the left drive wheel at a reverse speed while driving the right drive wheel at a forward speed, the left and right drive wheels are accordingly driven in different directions, thereby enabling the vehicle to be turned to the left (or to the right by analogy) at a zero turn radius while moving at a certain speed range in the forward (or, if desired, reverse) direction.
In some embodiments, the transmission control device comprises a moving, and preferably pivoting, guide member or members, and a mixing lever. The mixing lever is coupled to the continuously variable transmission devices through a suitable transmission linkage assembly, a preferred example of which is described hereinbelow. Preferably, the mixing lever is coupled to a hand-operated speed change lever similar to a stick shift lever. The speed change lever is employed to pivot or rotate the mixing lever about a first axis (e.g., a lateral or transverse axis) to select a speed or speed range and a direction (forward or reverse) at which the vehicle is to be driven. The speed change lever is also employed to select a neutral state. In a preferred embodiment in which the continuously variable transmission devices are based on a hydrostatic system, the neutral state corresponds to a stop state of the vehicle. The mixing lever also pivots or rotates about a second axis (e.g., a longitudinal axis) that is substantially perpendicular to the first axis. Movement of the steering handle actuates the guide member of the transmission control device to contact and move the mixing lever such that the mixing lever pivots about this second axis. Accordingly, both the steering handle and the speed change lever determine the position of the mixing lever, and in turn the state of the continuously variable transmission devices and, consequently, the respective angular velocities of the drive wheels.
In some embodiments, the transmission control device comprises a guide plate and a pair of spring-loaded guide members that cooperatively move the mixing lever in response to movement of the steering handle. For this purpose, the mixing lever extends through a distinctively shaped aperture of the guide plate and between the spring-loaded guide members. The position of the mixing lever within the aperture determines whether the vehicle moves in the forward or reverse direction, whether the vehicle is in a neutral state, the range of speed at which the vehicle moves, and whether the vehicle can be steered at a zero turn radius. The spring-loaded guide members are positioned so as to contact the mixing lever during initial movement of the steering handle, prior to contact by an edge of the guide plate aperture. Further movement of the steering handle in a desired steering direction eventually causes the edge of the guide plate aperture to also contact and move the mixing lever. By this configuration, the degree of response of the continuously variable transmission devices to the movement of the steering handle is gradually increased as the degree of movement of the steering handle is increased, thereby allowing greater control over the steering of the vehicle. The configuration also prevents the vehicle from being steered at a zero turn radius in response to only a slight movement of the steering handle while the vehicle is traveling at a high speed.
According to one embodiment, a steering control apparatus for a vehicle comprises a movable steering handle, first and second CVT devices for independently driving first and second drive wheels, respectively, a transmission control device, and first and second spring-loaded guide members. The transmission control device interconnects the steering handle and the first and second CVT devices, and comprises a mixing lever for controlling operations of the first and second CVT devices. The first and second guide members are disposed on opposite sides of the mixing lever. Movement of the steering handle in a first steering direction causes the first guide member to move the mixing lever in a first actuating direction, and movement of the steering handle in a second steering direction causes the second guide member to move the mixing lever in a second actuating direction.
In one aspect of this embodiment, the transmission control device comprises a pivotable guide plate communicating with the steering handle. The guide plate comprises an endless guide groove defining an aperture through the guide plate. The guide groove includes first and second groove edges, and the mixing lever extends through the aperture. Movement of the steering handle beyond a set value in the first steering direction causes the first groove edge to move the mixing lever in the first actuating direction, and movement of the steering handle beyond a set value in the second steering direction causes the second groove edge to move the mixing lever in the second actuating direction. Preferably, the first and second guide members are positioned relative to the guide plate for contacting the mixing lever prior to the first and second groove edges in response to movement of the steering handle. Preferably, the first and second guide members are mounted to the guide plate.
In another aspect of this embodiment, the apparatus comprises a change lever communicating with the mixing lever for pivoting the mixing lever into selected transmission drive positions. Preferably, the change lever is connected to the mixing lever for movement thereof in a longitudinal direction, and the first and second guide members are oriented relative to the mixing lever for movement thereof in a lateral direction substantially transverse to the longitudinal direction.
According to another embodiment, a steering control apparatus for a vehicle comprises a movable steering handle, first and second CVT devices for independently driving first and second drive wheels, respectively, a guide plate communicating with the steering handle and pivotable thereby, and a mixing lever. The guide plate comprises an endless guide groove including first and second groove edges and defining an aperture. The aperture comprises a narrow end area, a wide end area, a wide medial area adjacent to the wide end area, and a tapering area between the narrow area and the medial wide area. The mixing lever extends through the aperture and is selectively positionable in each area of the guide plate aperture. The mixing lever is connected to the first and second CVT devices for controlling respective operations thereof, wherein movement of the steering handle in a first steering direction causes the first groove edge to move the mixing lever in a first actuating direction and movement of the steering handle in a second steering direction causes the second groove edge to move the mixing lever in a second actuating direction.
According to one aspect of these embodiments, the mixing lever communicates with the first and second CVT devices such that the first and second CVT devices are neutral when the mixing lever is positioned in the medial wide area, the first and second CVT devices actively drive the first and second drive wheels in a first forward speed range when the mixing lever is positioned in the tapering area, the first and second CVT devices actively drive the first and second drive wheels in a second forward speed range when the mixing lever is positioned in the narrow end area, and the first and second CVT devices actively drive the first and second drive wheels in a reverse speed range when the mixing lever is positioned in the wide end area.
According to another aspect of these embodiments, the mixing lever communicates with the first and second CVT devices such that, when the mixing lever is positioned in the tapering area of the guide plate aperture, one of the CVT devices drives one of the drive wheels in a forward direction and the other CVT device simultaneously drives the other drive wheel in a reverse direction in response to movement of the steering handle beyond a set value in either the first or second steering direction.
According to yet another embodiment, a vehicle with transmission-controlled steering comprises a movable steering handle, first and second drive wheels, first and second CVT devices for independently driving the first and second drive wheels, respectively, a transmission control device, and first and second spring-loaded guide members. The transmission control device interconnects the steering handle and the first and second CVT devices, and comprises a mixing lever for controlling operations of the first and second CVT devices. The first and second spring-loaded guide members are disposed on opposite sides of the mixing lever. Movement of the steering handle in a first steering direction causes the first guide member to move the mixing lever in a first actuating direction, and movement of the steering handle in a second steering direction causes the second guide member to move the mixing lever in a second actuating direction. Preferably, the vehicle comprises one or more caster wheels that are turnable independently of the steering handle so as to facilitate steering the vehicle at a zero turn radius.
According to still another embodiment, a vehicle with transmission-controlled steering comprises a movable steering handle, first and second drive wheels, first and second CVT devices for independently driving the first and second drive wheels, respectively, a guide plate communicating with the steering handle and pivotable thereby, and a mixing lever. The guide plate comprises an endless guide groove defining an aperture. The aperture comprises a narrow end area, a wide end area, a wide medial area adjacent to the wide end area, and a tapering area between the narrow area and the medial wide area. The guide groove includes first and second groove edges. The mixing lever extends through the aperture and is selectively positionable in each area of the guide plate aperture. The mixing lever is connected to the first and second CVT devices for controlling respective operations thereof. Movement of the steering handle in a first steering direction causes the first groove edge to move the mixing lever in a first actuating direction, and movement of the steering handle in a second steering direction causes the second groove edge to move the mixing lever in a second actuating direction.
A method for steering a vehicle is also provided. Output power produced by a motor is coupled to first and second drive wheels through first and second CVT devices, respectively. A steering handle is moved in a selected steering direction to pivot a transmission control device comprising first and second spring-loaded guide members and a mixing lever extending between the first and second guide members. One of the guide members moves the mixing lever. Movement of the mixing lever causes the first CVT device to drive the first drive wheel at a first angular velocity, and the second CVT device to drive the second drive wheel at a second angular velocity that is different from the first angular velocity. The method can be implemented such that the first angular velocity has a forward direction component and the second angular velocity has a reverse direction component, thereby causing the vehicle to be steered according to a zero turn radius.
In one aspect of this method, the transmission control device comprises a guide plate pivotable therewith, and the guide plate comprises an endless guide groove defining an aperture through the guide plate. The guide groove comprises first and second opposing groove edges, and the mixing lever extends through the aperture between the groove edges. The steering handle is moved beyond a set value in the selected steering direction to cause one of the groove edges to move the mixing lever in cooperation with the one guide member. In another aspect, the guide groove defines a plurality of distinct operating areas of the aperture. The mixing lever is positioned at a selected one of the operating areas to select a running speed and an alternative forward or backward direction of movement for the vehicle during turning of the vehicle. Preferably, the aperture comprises a narrow-width area and a tapering-width area. The narrow-width area is disposed relative to the mixing lever so as to prevent the vehicle from being steered at zero turn radius when the mixing lever is positioned within the narrow-width area, and the tapering-width area is disposed relative to the mixing lever so as to permit the vehicle to be steered at zero turn radius when the mixing lever is positioned within the tapering-width area. Preferably, movement of the steering handle in the selected direction while the mixing lever is positioned in the tapering-width area causes one of the guide groove edges corresponding to the tapering-width area to move the mixing lever in both a transverse direction and a longitudinal direction, whereby the vehicle is both steered and slowed.
It is therefore an object of the present invention to provide an apparatus and method for steering a vehicle through control of its transmission and in such a manner that the vehicle can turn according to a zero turn radius.